Heat exchanger with varied louver angles

ABSTRACT

A heat exchanger assembly includes spaced apart tubes and a fin. The fin extends between and in thermal contact with adjacent tubes. The fin defines a planar portion between adjacent tubes. The planar portion defines a louver. The louver defines an axis about which the louver is rotated relative to the planar portion when the louver is formed. A middle portion of the louver is rotated about the axis to a first angle. A top portion of the louver is rotated about the axis to a second angle greater than the first angle such that the louver angle is varied along the axis. The louver may be characterized along the axis by a continuous transition of angle from the first angle to the second angle. A bottom portion of the louver may be rotated about the axis to a third angle greater than the first angle.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part application and claims thebenefit under 35 U.S.C. §120 of U.S. patent application Ser. No.13/834,355 filed 15, Mar. 2013 and titled SPLIT MINI-LOUVERED FINS,which is a continuation-in-part application U.S. patent application Ser.No. 12/221,705 filed 06, Aug. 2008 and titled LOUVERED AIR CENTER FORCOMPACT HEAT EXCHANGER, now abandoned, the entire disclosure of both ishereby incorporated herein by reference.

TECHNICAL FIELD OF INVENTION

This disclosure generally relates to a heat exchanger assembly, and moreparticularly relates to a louvered fin where an angle of each louver isvaried such that the angle of the louver varies along the length or axisof the louver.

BACKGROUND OF INVENTION

Air cooled heat exchanger assemblies are used in automobiles to transferheat from various working fluids such as engine coolant, enginelubricating oil, air conditioning refrigerant, and transmission oil. Atypical air cooled heat exchanger assembly includes a plurality of fluidconveying tubes hydraulically connecting an inlet header to an outletheader, and corrugated louvered fins disposed in a zig-zag patternbetween adjacent fluid tubes. Louvers are provided to increase the heattransfer efficiency of the heat exchanger assembly.

SUMMARY OF THE INVENTION

In accordance with one embodiment, a heat exchanger assembly isprovided. The assembly includes a plurality of parallel spaced aparttubes and a fin. The tubes are configured to convey coolant within thetubes. The fin extends between and in thermal contact with adjacenttubes. The fin defines a planar portion between the adjacent tubes. Theplanar portion defines a louver. The louver defines an axis about whichthe louver is rotated relative to the planar portion when the louver isformed. A middle portion of the louver is rotated about the axis to afirst angle. A top portion of the louver is rotated about the axis to asecond angle greater than the first angle such that the louver angle isvaried along the axis.

In another embodiment, the louver is characterized along the axis by acontinuous transition of angle from the first angle to the second angle.

In yet another embodiment, a bottom portion of the louver is rotatedabout the axis to a third angle greater than the first angle.

Further features and advantages will appear more clearly on a reading ofthe following detailed description of the preferred embodiment, which isgiven by way of non-limiting example only and with reference to theaccompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

The present invention will now be described, by way of example withreference to the accompanying drawings, in which:

FIG. 1 is a perspective front view of a heat exchanger assembly equippedwith fins in accordance with one embodiment;

FIG. 2 is a perspective view of a known fin;

FIG. 3 is a close-up view of the known fin of FIG. 2;

FIGS. 4A, 4B, and 4C show a louver configuration for a fin of theassembly of FIG. 1 in accordance with one embodiment;

FIG. 5A, 5B, and 5C show a louver configuration for a fin of theassembly of FIG. 1 in accordance with one embodiment; and

FIG. 6 is a sectional end view of a pair of louvers of a fin of theassembly of FIG. 1 in accordance with one embodiment.

DETAILED DESCRIPTION

FIG. 1 illustrates a non-limiting example of a heat exchanger assembly,hereafter referred to as the assembly 20. The assembly 20 includes afirst manifold 22 and a second manifold 24 spaced apart from and in asubstantially parallel relationship with the first manifold 22. Thefirst manifold 22 and the second manifold 24 are configured to receive aplurality of parallel spaced apart tubes 28 configured to convey, forexample, coolant through the tubes 28 between the first manifold 22 andthe second manifold 24. The tubes 28 are typically inserted into slots26 of the first manifold 22 and the second manifold 24 and sealed to themanifolds by, for example, brazing, as will be recognized by those inthe art. A plurality of corrugated fins 32 is disposed between and inthermal contact with adjacent instances of the tubes 28 for increasedheat transfer efficiency between the fluid in the tubes 28 and theairflow 30 through the assembly 20, which may be urged by a fan (notshown). The tubes 28 and the corrugated fins 32 between the tubes 28generally cooperate to define a core 34 of the assembly 20. Spacesbetween adjacent planar portions of the corrugated fins 32 and the tubes28 cooperate to define a plurality of channels 36 that direct theairflow 30 through the core 34.

FIGS. 2 and 3 illustrate a prior art corrugated louvered fin, hereafterthe fin 250, equipped with single louvers 252 along a planar portion 254of the fin 250. The fin 250 is formed from a thin strip of heatconductive material into radiused portions 256 and planar portions 254that are alternately continuously arranged to define a corrugation. Eachof the planar portions 254 includes a leading edge 258 oriented into theoncoming direction of the airflow 30, an opposite trailing edge 260spaced from the leading edge 258, and a plurality of louvers 252therebetween. Each louver 252 is defined by a louver segment 262oriented at a predetermined angle relative to the planar portion 254between a pair of slits 264. On opposite ends of the louver segment 262is a juncture 266 that transitions the louver segment 262 to the planarportion 254. Each louvers 252 is generally formed by pivoting the louversegments 262 about the junctures 266 (i.e. an axis that extends betweenthe junctures 266) such that the louver segments 262 are oblique orangled relative to the planar portion 254. The pivoting of the louversegment 262 about the juncture 266 defines a twisted transition thatconnects the single louver 252 to the planar portion 254. The louver 252defines a front edge 268 oriented toward the direction of airflow 30 andan opposite rear edge 270. The front edges 268 of the louvers 252 aresubstantially parallel with each other and may be parallel with theleading edge 258 of the planar portion 254. That is, the angle of thelouver segments 262 is relatively constant along the length of thelouver segments 262 or relatively constant along the axis that extendsbetween the junctures 266.

It was discovered that the amount of heat transferred from a heatexchanger assembly (e.g. the assembly 20) could be increased if theangle of the louvers was varied along the axis of the louver as opposedto keeping the angle fixed as shown in FIGS. 2 and 3. In particular, theheat transfer was increased if the angle relative to the planar portionof the end portions of a louver segment was increased relative to themiddle portion of the louver segment. U.S. Pat. No. 6,672,376 issuedJan. 6, 2004 to Shembekar et al. shows louvers with an abrupt twist inthe middle of each louver. U.S. Pat. No. 5,730,214 issued Mar. 24, 1998to Beamer et al. shows flat louvers with angles set in accordance withthe location of the louver on a fin relative to the direction ofairflow. As will become apparent in the description that follows, theassembly 20 described herein is equipped with louvers characterized by alouver angle that varies along the length or axis of the louver. It willalso be apparent that the louvers described herein are not comparable tothe louvers shown by Shembekar or Beamer.

FIGS. 4A, 4B, and 4C illustrate a non-limiting example of a portion of afin 32 suitable for use in the assembly 20 of FIG. 1. As shown in FIG.1, the fin 32 extends between and is in thermal contact with adjacenttubes 28. The fin 32 defines a planar portion 40 (FIG. 4A, 4B, and 4C)between the adjacent tubes. The planar portion 40 includes or defines aplurality of louvers, hereafter the louver 42. Each louver defines anaxis 44 about which the louver 42 is rotated relative to the planarportion 40 when the louver 42 is formed. Each louver includes or definesa middle portion 46 shown in cross section in FIG. 4C, and a top portion48 shown in cross section in FIG. 4B. That is, Figs. 4B and 4C show aperspective where the axis 44 is normal or perpendicular to the page onwhich FIGS. 4B and 4C are shown.

As mentioned above, it was discovered that heat transfer of the assembly20 could be improved if the middle portion 46 and the top portion 48 haddifferent angles relative to the planar portion 40. Preferably, themiddle portion 46 of the louver 42 is rotated about the axis 44 to afirst angle 50, and the top portion 48 of the louver 42 is rotated aboutthe axis 44 to a second angle 52 that is greater than the first angle50. By this configuration, the angle of the louver 42 is varied alongthe axis 44.

In one embodiment the angle of the louver 42 at any point along the axis44 may be continuously varied along the axis 44 so that the transitionfrom the top portion 48 to the middle portion 46 is a smooth transition.That is, the louver 42 may be characterized along the axis 44 by acontinuous or smooth transition of angle from the first angle 50 to thesecond angle 52. This does not preclude having the angle be fixed for aportion of the length of the axis 44. For example, the middle portion 46may be defined to be the middle third of the louver 42, and that middlethird may all be at the same angle (e.g. the first angle 50) and notcontinuously varied through that middle third.

It may also be advantageous if a bottom portion 54 of the louver 42 isrotated about the axis 44 to a third angle 56 greater than the firstangle 50. Such a configuration would cause an end view or side view ofthe louver 42 to have the appearance of an hour glass shape (FIG. 6),even though the actual width of the louver 42 is substantially constant.In one embodiment, the third angle 56 is substantially equal to thesecond angle 52. As used herein, substantially equal means within thetolerance of manufacturing, e.g. +/−3 degrees of angle. Also, the shapeof the louver 42 may be symmetrical about the middle portion 46.Furthermore, like the embodiment described above, the louver 42 may beconfigured so that the louver 42 is characterized along the axis 44 by acontinuous transition of angle from the second angle 52 to the firstangle 50, and from the first angle 50 to the third angle 56.

FIGS. 5A, 5B, and 5C illustrate another non-limiting example of aportion of a fin 32 of the assembly 20. The louvers in this example aresometimes referred to as split louvers where a first louver 60 definesor is oriented about a first axis 64 offset from the planar portion 40in first direction 68, and a second louver 62 defines or is orientedabout a second axis 66 offset from the planar portion 40 in a seconddirection 70 opposite the first direction 68. While not subscribing toany particular theory, the split louvered fins have been observed toincrease heat transfer efficiency relative to the single louverarrangement shown in FIGS. 4A-C. It is believe that the increase is dueto allowing greater louver penetration into the channels 36 defined byeach pair of planar portions to increase the distance that the airflow30 has to travel through the core 34 and thereby increase the number ofboundary layer interruptions that the airflow 30 has to encounter, whileminimizing the pressure drop. As with the previous example, each louverincludes or defines a middle portion 72 at a first angle 50 relative tothe planar portion 40 as shown in cross section in FIG. 5C, and a topportion 74 at a second angle 52 relative to the planar portion 40 asshown in cross section in FIG. 5B. That is, FIGS. 5B and 5C show aperspective where the first axis 64 and the second axis 66 are normal orperpendicular to the page on which FIGS. 5B and 5C are shown. As withthe prior example shown in FIGS. 4A-C, the second angle 52 is preferablygreater than the first angle 50.

By way of example and not limitation, if the distance between adjacenttubes is 5.5 mm, a suitable length of the middle portion (46, 72) is 2.6mm, and a suitable length of the top portion (48, 74) and the bottomportion (54, 78) is 1.0 mm. For this size louver, a suitable value forthe first angle 50 is 23 degrees, and a suitable angle for the secondangle 52 and/or the third angle is 35 degrees. It is recognized thatother angles may be optimum for different dimensioned fins. It is alsorecognized that each louver of a plurality of louvers may have anoptimum angle. For example, the louvers near the middle of the fin mayadvantageously have a greater angle than louvers near the leading edgeand the trailing edge of the fin 32.

FIG. 6 illustrates a non-limiting example of the fin 32 that includes ordefines a first planar portion 40A adjacent to a second planar portion40B. The fin 32 is also configured to define a radiused portion 76 sothe first planar portion 40A is parallel to the second planar portion40B. By having a large enough radius, adjacent planar portions can beparallel. However, if the radius is too large, the density of the finsmay be undesirably reduced Having adjacent planar portions in a parallelorientation is advantageous as airflow through the channels 36 definedby the adjacent planar portions is more uniform from top to bottom. Ifthe radius was smaller, as is in vogue today, the adjacent planarportions could not be parallel, so airflow inside the channel near theradiused portion would be more restricted than in the part of thechannel that was away from the radiused portion. Also, the relativelylarge fin tip radius of a radiused portion 76 as compared to thedistance between the two adjacent planer portions of adjacent louversallows for maximizing the second angle 52 and the third angle 56relative to the first angle 50. This significantly enhances airflowbetween the louver passages at the top and bottom of the fin, and thusimproving the resulting heat transfer. A concomitant benefit realizedwith the variable louver angle fin combined with large tip radius isthat the first few (2-3) louvers in the second half of the fin, i.e. thefins after the mid-section (i.e. the first planer portion 40A) which aretypically starved of airflow and heat transfer in conventional fin, haveimproved heat transfer due to improved airflow.

Accordingly, a heat exchanger assembly (the assembly 10) is provided.The twisting of each louver (42, 60, 62) helps to optimize the angle ofthe louver for local airflow conditions. That is, different airflowrates may exist at the middle portion as compared to the top or bottomportion, so varying the angle of the louver along the length of thelouver helps to improve heat transfer from the fin 32 to the airflow 30.

While this invention has been described in terms of the preferredembodiments thereof, it is not intended to be so limited, but ratheronly to the extent set forth in the claims that follow.

We claim:
 1. A heat exchanger assembly comprising: a plurality ofparallel spaced apart tubes configured to convey coolant therethrough;and a fin extended between and in thermal contact with adjacent tubes,wherein the fin defines a planar portion between the adjacent tubes, theplanar portion defines a louver, the louver defines an axis about whichthe louver is rotated relative to the planar portion when the louver isformed, and a middle portion of the louver is rotated about the axis toa first angle, wherein a top portion of the louver is rotated about theaxis to a second angle greater than the first angle such that the louverangle is varied along the axis.
 2. The assembly in accordance with claim1, wherein the louver is characterized along the axis by a continuoustransition of angle from the first angle to the second angle.
 3. Theassembly in accordance with claim 1, wherein a bottom portion of thelouver is rotated about the axis to a third angle greater than the firstangle.
 4. The assembly in accordance with claim 3, wherein the thirdangle is substantially equal to the second angle.
 5. The assembly inaccordance with claim 3, wherein the louver is characterized along theaxis by a continuous transition of angle from the second angle to thefirst angle, and from the first angle to the third angle.
 6. Theassembly in accordance with claim 5, wherein the third angle issubstantially equal to the second angle.
 7. The assembly in accordancewith claim 1, wherein a first louver defines a first axis offset fromthe planar portion in first direction, and a second louver defines asecond axis offset from the planar portion in a second directionopposite the first direction.
 8. The assembly in accordance with claim1, wherein the fin includes a first planar portion adjacent to a secondplanar portion, and the fin is configured to define a radiused portionso the first planar portion is parallel to the second planar portion.